Twenty-nine people are in hospital, most of whom suffered "flash burns", after the improvised explosive device went off at Parsons Green station in south-west London at around 8.20am. ITV News

A number of church leaders have issued a call to prayer after a crude device exploded on a crowded London Underground train, injuring 29 in what has been called a terrorist attack.

The New York Times reports that a manhunt is currently underway after the device exploded at 8:20 a.m. on an eastbound District Line train leaving the Parsons Green station in Southwest London. At least 29 people were hospitalized, but none had life-threatening injuries, according to hospital officials. British authorities said they are treating the blast as a terrorist attack.

On Twitter, religious leaders and organizations urged Christians worldwide to pray for those affected.

Hillsong Church pastor Brian Houston tweeted, "There's been an explosion at the tube station our staff use in London near our offices. (Parsons Green.) Let's pray urgently."

He later tweeted, "All our London staff are apparently safe and accounted for."

The Archbishop of Canterbury Justin Welby tweeted: "Praying for all those caught up in this morning's terror incident at #ParsonsGreen, especially those who have sustained injuries or trauma."

The London City Mission tweeted, "Please #prayforlondon this morning following a reported explosion on the District Line."

Archbishop of Westminster, Cardinal Vincent Nichols, said: "I am dismayed at yet another cowardly attack on innocent people, including young children, as they were commuting to work and school this morning. I pray for all who were injured in the blast and in the ensuing stampede, and for all who were affected by the incident. May God grant them and all Londoners peace and strength our resolve to stand against such evil acts."

He praised the emergency services and all those who rushed to help those affected.

"The generous actions of those who rushed to tend to the wounded and those who were in shock demonstrate all that is good in humanity as a small number seek to divide our society. We should all be alert, but remain calm."

Dr Graham Tomlin, Bishop of Kensington, said: "In recent months, London has repeatedly shown strength and solidarity in the face of adversity. We had truly hoped we would not be here again so soon."

Prime Minister Theresa May has blasted the "cowardly attack" and said the UK's terror threat would not be raised to the highest "critical" level as it was after the Manchester Arena attack, and remained at "severe".

Home Secretary Amber Rudd condemned the blast, saying: "Once more people going about their everyday lives have been targeted in a callous and indiscriminate way. My thoughts are with all those injured and affected."

She paid tribute to the work of the emergency services and urged Londoners "to remain alert and assist the police and emergency services as much as they can

This is the fifth terrorism incident of 2017 in which an attack has taken place, notes the BBC, but is the only one this year in which nobody has died.